Auto-measuring universal meter

Abstract

An auto-measuring universal meter is disclosed. The auto-measuring universal meter includes a main unit having a display and a single button. A pair of test probes is electrically connected to the main unit in a removable manner to detect a first input signal; an inductive clamp is formed on and electrically connected to the main unit for gripping a current-carrying conductor to detect a second input signal indicative of an alternating/direct current flowing through the current-carrying conductor. The main unit is designed so as to take measurement of the input signals in a self-judging mode based on the presence of and/or the differences between the input signals so that the alternating/direct current can also be measured.

1. An auto-measuring universal meter, comprising:
 a main unit having a display and a single button; 
 a pair of test probes electrically connected to said main unit in a removable manner to detect a first input signal; and 
 an inductive clamp formed on and electrically connected to said main unit for gripping a current-carrying conductor to detect a second input signal indicative of an alternating/direct current flowing through said current-carrying conductor; 
 wherein said main unit measures said input signals in a self-judging mode based on the presence of and/or the differences between said input signals so that said alternating/direct current is measured, 
 wherein said self-judging mode further includes an alternating voltage measuring mode, a direct voltage measuring mode, an alternating current measuring mode, a resistance measuring mode, and a diode measuring mode, 
 wherein said main unit measures said input signals in said self-judging mode based on a criterion that said first input signal takes priority for measurement over said second input signal, 
 wherein said main unit has an internal circuitry comprising:
 an attenuation circuit for receiving said first input signal from said pair of test probes and then sending an attenuated signal both to a first rectifier and filter circuit and to a first filter circuit; said first rectifier and filter circuit sending out a DC signal indicative of an alternating voltage, and said first filter circuit sending out a DC signal indicative of one of a direct voltage, a measurable resistance, and a diode; 
 a current-sensing circuit for sensing an electric current flowing through said current-carrying conductor and then sending a signal both to a second rectifier and filter circuit and a second filter circuit, said second rectifier and filter circuit sending out a DC signal indicative of an alternating current, and said second filter circuit sending out a DC signal indicative of a direct current; 
 a protection circuit electrically coupled to said pair of test probes; 
 a constant current supply circuit for supplying said protection circuit with a constant current necessary during the measurement in said resistance measuring mode; 
 a constant voltage supply circuit for supplying said protection circuit with a constant voltage necessary during the measurement in said diode measuring mode; 
 a resistance-detecting circuit electrically coupled to said protection circuit for sending out a signal indicative of the presence of either of said measurable resistance and said diode between said test probes; 
 a switching circuit controlled so as to selectively receive at most two of said signals sent from said rectifier and filter circuits, said filter circuits, and said resistance-detecting circuit at any moment and to send out a signal indicative of one of said alternating/direct voltage, said alternating/direct current, said measurable resistance, and said diode; 
 an A/D converter for converting a measured result carried by said at most two signals from an analog form to a digital form; 
 an electronic controller for transforming said measured result in said digital form to a format necessary for said display and consistent with one of said measuring modes which is used at that moment; and 
 a brightening circuit for detecting the environmental darkness and for brightening the background of said display in response to a signal from said electronic controller. 
 
 
   
   
     2. The auto-measuring universal meter as claimed in  claim 1 , wherein said switching circuit is controlled by said electronic controller so as to operate according to said one of said measuring modes which is used at that moment. 
   
   
     3. The auto-measuring universal meter as claimed in  claim 1 , wherein said electronic controller controls the operation of said switch circuit by determining which of said measuring modes is being used at that moment as a result of a judgment based on the different natures and/or different magnitudes of said input signals, and wherein said electronic controller changes the operation of said display among said visual modes in response to a signal with a particular duration sent from said single button. 
   
   
     4. The auto-measuring universal meter as claimed in  claim 1 , wherein said brightening circuit sends a signal to said electronic controller when said main unit is operated in a dark place and then to brighten said background of said display in response to a signal sent back from said electronic controller.